The present invention relates to a coating composition, especially, relates to an aqueous coating composition with improved liquid stain repellency.
Stain resistance/removal is one of the key performances requirements for coating films. The stain resistance/removal refers to the resistance to stain, difficulty of being wetted by stain, difficulty of being adhered by stain and easiness of stain removal, includes but is not limited to, hydrophilic stain resistance, hydrophobic stain resistance, hydrophilic and hydrophobic stain removal, and hydrophilic stain repellency, such as beading effect to hydrophilic stain.
Currently, beading effect is achieved by adding additives to reduce surface tension of paint films. Among them, wax emulsion is the most popular one. However, the beading efficiency of the emulsified wax which can provide beading effect is because wax can migrate onto the dried coating film surface and reduce surface tension, which will make the stains hardly wet coating film. This phenomenon is called stain repellency or beading effect. Anything stops wax migrating onto the coating film surface will reduce beading efficiency. So it is not difficult to understand that the beading efficiency of wax emulsion is influenced substantially by the coating formulation. For example, when PVC of formulations is increased, higher level of wax emulsion has to be used to achieve beading effect, but such high level of wax emulsion usage compromises other performances of coating films.
Surprisingly, it has been found that using polymer-encapsulated pigments partially or fully replaces mineral pigments in a water based paint formulation can improve the beading efficiency of wax emulsions. On the other side, the wax level could be decreased to avoid compromising performance of coating film and save cost.
U.S. Pat. No. 7,579,081 B2 disclosed polymer-encapsulated pigments that include certain pigments substantially encapsulated with a first and a second polymer, and a coating composition comprising the polymer-encapsulated pigments. Inventors for U.S. Pat. No. 7,579,081 B2 never considered the possibility of combining the use of the disclosed polymer encapsulated pigment with wax in coating compositions to achieve incredible stain resistance/removal function.
It is therefore, still desired in the art to get to a novel coating composition, especially, aqueous coating composition that has more efficient stain resistance/removal function and also under a reasonable and controllable cost.